Found a fix for PC. via youtube:

"Go to steam right click mw3 multiplayer then click properties.

then click local files, then click verify integrity of game cache, once downloaded it should come up saying mw3 successfully downloaded then play and it worked for me. i hope this works for u"

It worked like a charm for me.  It was a real bother with this problem.  Sorry for the ps3 and xbox folks.

I live 30 minutes outside downtown chicago and i cannot find a game. I have friends all over the country that are having the same problem. If i matchmake by myself then i can find games but the second i try searching for a game with a party games are almost impossible to find.

I have seen at least 20 post about this issue, guess what, they do not give a **** about the problem,,,,that is why now day 4 no game found....